XKeyCaps 2.46

It opens a window that looks like a keyboard; moving the mouse over a key shows what KeySyms and Modifier bits that key generates. Clicking on a key simulates KeyPress/KeyRelease events on the window of your choice. It is possible to change the KeySyms and Modifiers generated by a key through a mouse-based interface. This program can also write an input file for xmodmap to recreate your changes in future sessions.